1. Field of the Invention
My invention relates in general to energy conservation and waste recovery at phosphorus furnaces, and it deals more particularly with a process and apparatus for waste recovery at phosphorus furnaces by low energy agglomeration thereof in a matched particulate component which may be used as a recharging component for such a furnace and for other purposes.
Elemental phosphorus is produced by smelting a mixture of mineral phosphate, coke, and silica rock in a submerged arc electric furnace. The mineral phosphate is usually agglomerated at high temperatures by processes similar to those employed in the metallurgical industry. Development of the phosphorus furnace process is described in a TVA publication ("Production of Elemental Phosphorus by the Electric-furnace Method," R. B. Burt and J. C. Barber, Chemical Engineering Report No. 3, 1952, National Fertilizer Development Center, Muscle Shoals, Ala. 35660). Development of agglomeration processes for phosphorus furnace feed materials is given in another TVA publication ("Agglomeration of Phosphate for Furnace Use," E. L. Stout, Chemical Engineering Report No. 4, National Fertilizer Development Center, Muscle Shoals, Ala. 35660).
It is noted that much particulate matter is emitted during high temperature agglomeration of the phosphate. About 12 percent of the fluorine combined in the phosphate ore is evolved, although this percentage will vary with the temperature. Much energy is expanded in air pollution abatement, and water waste problems are created. Large quantities of fuel are consumed.
No fluorine is emitted with low temperature agglomeration of the mineral phosphates, and particulate emission is small. The energy requirement is reduced from the range of 2.5.times.10.sup.6 to 4.times.10.sup.6 million Btu per ton of agglomerates to about 800,000 Btu.
Metallurgical coke is generally purchased for use as a reducing carbon in phosphorus furnaces. However, the coke fines (minus 10-mesh material) adversely affects furnace operation. About fifteen percent of the purchased coke is fines. When the fines are removed, a solid waste problem is created unless some use can be found for this material.
I have discovered that mineral phosphates can be agglomerated at low temperature by a novel application of surface tension forces. Coke fines may be agglomerated at low temperature by similar application of surface tension forces to prepare properly sized material for use as a reducing carbon in the phosphorus furnace according to the present invention. Also, the agglomeration processes may be applied to other carbonaceous materials, such as calcined anthracite, and thereby relieve the current shortage of metallurgical coke.
My invention deals with the recovery of small sized coke material and condenser bleed-off water at phosphorus furnaces. The small sized coke is agglomerated by a new process, as described herein, and this will permit the coke to be used in phosphorus furnaces as a reducing carbon. Condenser bleed-off water, after treatment, can be used as a feedstock in making fluid fertilizers. Sludge acid separates from merchant-grade wet-process phosphoric acid, and this waste material can be used as a binder in the new agglomeration process of this invention.
Likewise, flotation tailing is obtained when phosphate ores are beneficiated. This new agglomerating process will permit this waste to be combined with phosphate concentrates and agglomerated to make a self-fluxing furnace charge material. The improved agglomeration process makes it possible to use phosphorus furnace charge materials with matched average sizes and size distributions. As a result, segregation in the furnace is essentially eliminated and furnace pressure fluctuations reduced. The overall result is less electric energy used for smelting and less loss of elemental phosphorus from inleakage of air.
2. Discussion of Prior Art
After a competent search of the state of the art, no existing process and product of waste recovery at phosphorus furnaces was disclosed embodying the principles of the present invention directed to such purposes, and no bench scale apparatus of the type used herein for such agglomeration was revealed. The prior art discloses the following U.S. patents:
U.S. Pat. No. 2,040,081, Mar. 12, 1936, Harry A. Curtis. A process is disclosed in the patent for the agglomeration of finely ground phosphate in a pug mill. This invention relates to the process of agglomerating fine phosphate rock from an original ore.
U.S. Pat. No. 2,741,545, Apr. 10, 1956, F. T. Nielsson. This is a forerunner of all of the ammoniation-granulation patents in the manufacture of fertilizer.
U.S. Pat. No. 3,012,874, Dec. 12, 1961, A. B. Phillips, et al. In this patent calcium metaphosphate is granulated with hot water.
U.S. Pat. No. 3,034,883, May 15, 1962, T. P. Hignett, et al. This is a process for the agglomeration of a fertilizer mixture where superphosphate is produced in place in the binder.
U.S. Pat. No. 3,113,858, Dec. 10, 1963, A. V. Slack, et al. This is a patent which deals with the production of suspension fertilizers.
U.S. Pat. No. 3,177,062, Apr. 6, 1965, T. P. Hignett, et al. This is a process for granulating ground phosphate whereby elemental sulfur is the binder.
U.S. Pat. No. 3,202,744, Aug. 24, 1965, J. C. Barber, et al. In this patent, a phosphorus sludge is used as a binder to briquet phosphorus furnace feed.
U.S. Pat. No. 3,335,094, Aug. 8, 1967, W. J. Darby. This is a process for preparing a briquetted mixture of phosphate, silica and coke having a high electrical resistance.
U.S. Pat. No. 3,464,809, Sept. 2, 1969, G. C. Hicks. This is a process for making granular ammonium sulfate in the ammoniator-granulator.
U.S. Pat. No. 3,813,233, May 28, 1974, L. A. Kendrick, Jr. This is a process for making a high-analysis suspension fertilizer from merchant-grade wet-process phosphoric acid.